It is desirable that sealants, coatings, and adhesives used in aviation and aerospace applications exhibit flexibility, fuel resistance, and high-temperature resistance. In general, these properties may be accomplished by incorporating polythioether linkages into the backbone of polymer resins.
Flexible, fuel resistant epoxy-terminated polysulfides have been developed which exhibit good fuel resistance. These compounds are typically formed using epichlorohydrin as a reactant. Epichlorohydrin is extremely toxic and the synthesis of epoxy-terminated polysulfides using epichlorohydrin generates corrosive hydrolysable chlorine (“HYC”) as an undesirable byproduct. Further, the compounds formed using epichlorohydrin incorporate un-reacted epichlorohydrin that must be removed by thorough washing. Such epoxy-terminated polysulfides typically exhibit a relatively high viscosity of about 30 poise at 25° C. and a broad epoxy equivalent weight range.
There is a need for improved flexible, fuel resistant, and high-temperature resistant epoxy-capped polythioethers and compositions of epoxy-capped polythioethers synthesized by methods that are environmentally compatible and that do not produce toxic byproducts. Further, it is desirable to produce epoxy-capped polythioethers with a controlled and narrow epoxy equivalent weight range.
The epoxy-capped polythioethers of the invention formed by the addition of thiol across the double bond of a monoepoxide comprising an olefinic group are flexible, fuel resistant and the high-conversion synthesis does not generate hydrolysable chlorine and avoids the use of epichlorohydrin. The epoxy capped polythioethers of the invention exhibit a controlled and narrow epoxy-equivalent weight distribution.
The present invention is also directed to amine/hydroxy-capped polythioethers formed from such epoxy-capped polythioethers.